The present invention provides an inhibitor for lens hardness containing a compound represent by formula (I) or a salt thereof, and/or a compound represent by formula (II) or a salt thereof:(in the formula, R1 and R4 are the same or different, represents a hydrogen atom, a halogen atom, a hydroxyl group, a mercapto group, a lower alkyl group, an lower acyl group, a lower alkoxy group, a carboxyl group, a carbamoyl group or a carbonylaminoacid group)(in the formula, R represents a hydrogen atom, or a lower alkyl group which may be substituted by an amino group, a hydroxyl group, a sulfanyl group or a carboxyl group, A represents a lower alkylene group,).本發明提供一種水晶體硬化抑制劑,其含有式(I)所示之化合物或其鹽、及/或式(II)所示之化合物或其鹽:(式中,R1至R4係相同或相異,表示氫原子、鹵素原子、羥基、氫硫基、低級烷基、低級醯基、低級烷氧基、羧基、胺甲醯基或羰基胺基酸基)(式中,R表示氫原子,或者可經胺基、羥基、氫硫基或羧基取代之低級烷基,A表示低級伸烷基)。由於本案的圖皆為實驗數據,不足以代表本案。故本案無指定代表圖。
